A New Flagellate Percolomonas lacustris sp n. (Excavata, Percolozoa) from an Inland Saline Lake (Southeastern European Russia)

The external and internal morphology of a new species of excavate flagellate which inhabits the saline Novoe Lake (Orenburg oblast, Russia) is considered. A cell of the flagellate has four naked flagella (one long and three short) extending parallel to each other. The long and one short flagella terminate with an acroneme. Three microtubular bands reinforce the longitudinal ventral groove. The vesicular nucleus lies in the anterior part of the cell. The mithochondria have discoid cristae. The system of submembrane microtubules originates from the fibrils close to the kinetosome and extends to the end of the posterior cell. A small bulbous projection is seen at the tip of the end of the posterior cell. Dictyosomes of the Golgi apparatus are not found. The lifecycle includes spherical thick-walled cysts that have a single hole with a plug. The external structure of the cell and cysts of a similar species, Percolomonas cosmopolitus, is compared to that in P. lacustris. The new species differs from the known ones by the presence of a posterior bulbous projection, a hole and plug inside the cyst, an acroneme of one short flagellum, and other features.